In my UPS career I have worked as a loader for 6 years (1.5 PT), in several different operations (centers) in two different bldgs. In addition, I have done everything else on the preloader except DA and irregs. I know how hard the job is-what it's like to come to a packed boxline or blown out belt, given 4 or 5 hrs to load 2000 pcs (which ain't happenin'!), with then ungrateful, insensitive, little caring drivers coming in whining about your load (although most shouldn't, as they will have also come up through the operation rather than be hired off the street, and thus can empathise). I can agree hub workers, especially preloaders, are grossly underpaid for a very thankless job.
In my experience, one works harder as a preloader, in that it is more physically demanding; it is probably why I lost weight as a preloader; I am more or less steady weight-wise as a driver. However, being a driver service provider is harder, in that in addition to the physical demands there is a WHOLE lot more as well. There is far more mental (and even emotional) aspects to the job than you are aware of (how many preloaders do things comparable to someone cutting you off on the road? Have you ever been chased by a dog in the hub?) A bad day for you will only last 3 hrs, along with whatever stress, frustration and anxieties that comes with it; I say 2 because the first 1/2hr to hour you don't really know how bad your day will be, and thus don't have to worry about it. We can know our day is trash 5-7 hours before our shift ends, and if we have a bad day with airs our day could be ruined before it really begins. You won't get fired for heavy bins that don't want to empty; you can get fired for not properly managing your airs.
There is so much more responsibility and concerns that a driver has that I am not sure you can fathom. Even as a driver helper one wouldn't know the mental puzzles the driver has going on in his head, the decisions and concerns he is figuring out; all you think you know is "the lazy bum is making ME deliver everything", without understanding why.